Color photography



Sept. 16, 1924. 1,508,916

P D. BREWSTER COLOR PHOTOGRAPHY Filed June 6, 1914 s Sheets-Sheet 1 Q aa VMIAYI 4' 7 6 avwe M oz 3513A!) gimme? 6 1 8 0 1 R E T s w E R B D P.

. Sept, 16 1924.

coLo PHOTOGRAPHY Filed June 6, 1914 3 Sheets-Sheet 2 QMK Sept. v16 1924.

Filed June 6, 1914 3 Sheets-Sheet 5 n v "2 V vwe W601,

1404 4 4 -qIKGZAM Patented Sept. 16, 1924.

UNITED; STATES PATENT OFFICE.

PERCY D. BREWSTER, OF EAST ORANGE,

NEW JERSEY, ASSIGNOR, BY MESNE ASSIGN- MENTS, T0 BREWSTER PATENTSCORPORATION, OF NEW YO'RK, N. Y., A CORPORA- TION or NEW YORK.

COLOR PHOTOGRAPHY.

Application filed June 6 To all whom it may concern:

Be it known that. I, PERCY D. BREWSTER, a citizen of the United States,residing at East Orange, in the" county of Essex and State of NewJersey, have invented certain new and useful Improvements in ColorPhotography, of which the following is a full, clear, and exactdescription.

This invention pertains to so-called color photography, that is, theproduction of photographs in which objects are exhibited insubstantially their natural colors, and relates more particularly to thepositive photograph and the production of the same.

While the negative used niay be of any suitable type, I prefer one ofthe kind described in my prior Patents Nos. 1,145,968, issued July 13th,1915, 1,191,941, issued July 25th, 1916, and 1,208,739, issued December19th, 1916. In these patents I have described fully a number of specificways of producing color negatives of the kind referred to, but for thepresent purpose one example will be sufiicient, and may be brieflyexplained as follows. (It is to be clearly understood, however, that theprecise method of making the negative is immaterial to the presentinvention, and also that I use the term film i this film a pose).

to include as equivalents glass plates and other sheets or platessuitable for the pur- The raw film stock for the negative is, in theparticular example mentioned above, coated on both sides,on the frontwith a transparent emulsion sensitive only to blue and green, and on theback with an emulsion sensitive only to red and orange. Exposing(through a yellow filter to screen out the violet and ultraviolet raysand some of the blue) on a subject that we will suppose consists of ared circle on a background. of which the upper half is light blue-greenand the lower half is white, .the blue and green rays act on the frontemulsion while the red and orange rays passjhrough and act on the rearemulsion. Developing" the film in theusual way we find that on the frontemulsion the circle is transparent, with no deposit, while the'twohalves of the background are black, rendered by deposits of 1914. SerialNo. 843,351.

the same or substantially the same density.

On the back the circle is black, the bluegreen half of the background istransparent, and the white half is black. We now color these deposits,(by well understood chemical processes), the front being colored greenand the back red, so that on the front the background is green with thecircle remaining colorless; while on the back the circle is deep red,the lower half of the background is red and the upper half is colorless.By transmitted light the negative then shows the circle dark red, theupper half of the background dark green, and the lower half black due tothelight being unable to ass through both red and green. Our co ornegative is now completed, and can be used for printing any number ofpositives by the method described below, as can also other colortransparencies, for example, those made by the Autochrome and analogousprocesses.

In accordance with the present invention, the positive is a transparency(preferably bearlng an image on each side) to be viewed directlybytransmitted light or to be projected on a screen. At the present timethe invention is believed to find its most widely useful embodiment in'the form of cinematographic film, consisting of a series of picturesrepresenting successive phases of an object in motion. As such films arewell known, it is deemed unnecessary to illustrate the same herein.

In printing from a color negative upon a positive film which is coatedon both sides, the procedure preferably followed is such that on oneside of the film will be produced a photographic image by the action oflight of one color or group of colors, and on the other a photographicimage by the action of light of a difi'erent color or group of colors;

after which the two images are colored dif tography, .they will combineto produce a single image in substantially the natural colors of theobject. Several modes of procedure b which these results can be attainedwill now be described.

Referring to the accompanying drawings,

Fig. 1 shows in cross section a film of the type which I prefer for theproduction of the color positives.

Fig. 2 is a similar section showing combined with the film a ray-screenor filter which is useful or necessary under some conditions.

Fig. 3 is an edgewise view, on a large scale, of a positive film,illustrating a feature which may exist therein and which, under somecircumstances, is a disadvantage.

Fig. 4 is a diagrammatic view of an or-- dinary optical system forprojecting lantern slldes and moving pictures.

Fig. 5 is a diagrammatic view illustrating simple and convenient meansfor printing positives by projection of the negative image or images.

Fig. 6 is a similar view illustrating a convenient method of printing bycontact.

Fig. 7 is' a diagrammatic sectional planview of a camera (described indetail in my aforesaid Patent No. 1,208,739) which can be used forprinting positives by projecting two negative images upon opposite sidesof the positive film.

Fig. 7 is a diagrammatic sectional planview pf another camera of thegeneral type described in my application Ser. No. 815,153, capable ofuse for printing positives by projection.

Fig. 7 b is a plan view illustrating a positlve' film having images onits two sides, one larger than the other so that when the film 1Sprojected (by rays converging through the film to the projecting lens)the two images will combine and produce a single or unitary image on thescreen. Part of the upper coating or emulsion (carrying the upper image)and part of the celluloid stock or support are broken away to showclearly the image on the underside. Red is indicated by vertical andgreen by diagonal shading. Fig. 8 shows diagrammatically aprojectionsystem which can be used for projectmg positives possessingthe feature illustrated in Fig. 3.

Fig. 9 is a diagrammatic view showing means for printing (from asuitable negative) positives having the feature illustrated in Fig. 3.

Figs. 10 and 11 are respectively a sectional and plan view of one formof film. disclosed chiefly to a group of colors extending down, say, toand including yellow-green of the visible spectrum; in other words, agroup of colors above yellow. The other side of the support bears acoating 3 which is sensitive chiefly to red and orange, and possibly toyellow, but which may be panchromatically sensitive.

In accordance with my present invention, color positives may be printedfrom the negatives in various ways. Where the colored image is to beviewed directly the positive can, if the negative is suitable, beprinted by contact, as any ordinary lantern slide or cinematographicfilm is printed. In projection work, the optical system commonly used isillustrated diagrammatically in Fig. 4, in which light rays 4, 5, 6,emanating from a source (not shown) at the point 7, are refracted by thecondensers 8, 9, pass through the positive A in a suitable support 10,and are brought to focus upon a screen (not shown) by the projectinglens 11. It will be observed that, with the exception of the axial ray5. the rays converge from the condensers to the projecting lens. Hencerays 4 and 6, for example, pass through the emulsion 3 at points nearerthe center of the film than are the points at which the same rays passthrough the emulsion 2. The result is that if the two images areidentically the same in size on the film, that is, congruent save asseparated by the transparent support 1, the ray 4:, for example, willprojeet difierent points of the image. This feature is illustrated on alarger scale in Fig. 3, in which 12 and 13, at the ends of the dottedline, indicat corresponding points in the congruent images. In short,the image on the screen will not be unitary but will be double, outsideof the center of the picture, oneimage overlapping the other and thusimpairing the definition. In order to avoid this defect I provide forprinting the positive in such manner that the two images shall becongruent at the center, but shall diflerin size progressively fromcenter to margin, the rate of difference. being regulated, other thingsbeing equal, by the distance between the film and the projecting lens,so that corresponding points in the two images (the smaller image beingnext to the projecting lens) will be in the paths of their respectiverays. In that case the image on the screen will be unitary and thedefinition thereof will not be materially impaired, if at all. In otherwords, the image projected from the emulsion 2, and that proje ted fromthe emulsion 3, will be in substantially congru ent register on thescreen. When the two images on the film are of such character in respectto sizeas to give a unitary image, or congruent images. on the screenwhen projected in the ordinary way- (or by special means for use withpositives whose images are congruent throughout) they may be said to beregistered or in registry, these terms being used as generic expressionsin the apreadily seen that the image produced on the emulsion 2 will! besmaller than that on emulsion 3, and that, ray 5 being assumed to be theaxial ray, the two images will be congruent at the path of that ray.Such negatives can also be made by means of the camera shown in Fig. 7,as clearly explained in my Patent No.'1,208,739, hereinbefore mentioned.

Fig. 5 illustrates diagrammatically a simple and effective method forprinting positives to produce images inprojection registry, of the typein whichthe images are centrally congruent but are progressivelydifferent in size from center to margin. In this figure, the printingrays 14, 15, 16, emanating from a point 17, are refracted by thecondensers 18, 19, through the color negative B, whose image must ofcourse be non-congruent (except at the center) to the same degree as isdesired in the positive. Having passed through. the negative the raysare brought to focus by the lens 20 upon the raw positive A. It is clearthat the angularity of the rays striking the positive should be the sameas that of the rays with which the completed positive is to besubsequently projected, and hence the focal length of the lens- 20 isgoverned very largely by the focal length of the lens (for example 11)which is to be used in the projection apparatus. Usually the positivewill be of the same size as the negative, in which case the equivalentfocal length of the lens 20 will be one-half the distance between theposition of the completed positive and the projecting lens (11) inactual use. Then in. printing the positive the same size as the negativethe lens 20 will be at the same distance from the negative and from therawpositive as the projecting lens is (in actual use) from the completedpositive. This feature is illustrated roughly in Figs. 4 and 5, where itis seen that the angularity of the rays is the same in each case. Of.course the converse of the foregoing is truezIf the focal length of theprinting lens 20 is chosen arbitrarily, the projecting lens (11) must beof such focal length that in actual operation it can beused at adistance from the positive equal to twice the focal length of theprinting lens. I prefer, however, to adapt the printing method to theprojecting system since in that case the resulting positives can be usedin present projecting machines with little or no alteration thereof.

Where the conditions of subsequent use permit the positive images to beslightly larger than the negative images the positive may be printed incontact with the negative (having non-congruent images) in the mannerillustrated in Fig. 6, in which B and A are the negative'and positiverespectively. Here, as in the former case, the printing rays,represented by '21, 22, 23 from the lens 24, have the same angularity ashave the rays with which the completed positive is to be projected ,onthe screen, or vice versa.

I prefer to .make the positives with noncongruent images of the typedescribed, as

such positives can be used in existing projection lanterns with littleor no alteration thereof; but it is possible to project, with greatenlargement and satisfactory definition, positives which have theirimages congruent throughout. means for this purpose is illustrated inFig. 8, where A indicates such a positive.- The projecting rays 25, 26,27, emanating from 28, are brought to parallelism by a collimating lens29. Having passed through the positive A" the parallel rays are causedto converge by the lens 30 to the projecting lens 31 which brings themto a focus on the screen, not shown.

If the negative has congruent images the congruent-image positive can"be printed therefrom by simple contact, but to secure the desiredsharpness ofdefinition in the positive images the printing rays wouldbeas nearly parallel as possible. i

To produce non-congruent positive im ages from a congruent negative amethod analogous to that illustrated in Fig. 8 may be resorted to. Thus,in Fig. 9, B is the negative having images congruent throughout, whichnegative is arranged between two lenses as in the positive A' in Fig. 8.The rays 32, 33, 34 from the point 35 are rendered parallel by thecollimating lens 36,

and having passed through the negative are converged by the lens 37 tothe lens 38 which 'brings them to focus on the raw positive A. Inasmuchas the rays striking the film A from the lens 38 are divergent, it willbe seen that the area which they cover on the front emulsion (the onenext to the lens) will be smaller than the area covered by them on therear emulsion, thereby making the image on the front smaller than theone on the back; but where the axial'ray (33) passes through the filmthe two images will be congruent.

In printing by methods WhlCll require Convenient that the rays which areto affect the rear emulsion of the positive must pass through the frontemulsion, as in Figs. 5, 6 and 9, for example, the front emulsion mustbe sufliciently transparent to permit the passage of such rays throughit. In such case it is advantageous to make the green-sensitive emulsionthe transparent one, chiefly because an emulsion can readily be madehighly sensitive to green and other colors above yellow and at the -sametime pracgreen.

tically non-sensitive to red and orange; thus permitting the latter raysto pass through without being affected by them. In any case, thetransparent emulsion should have as high degree of transparency aspossible, both to pass the greatest amount of light, and to minimizespreading or diffusion of the transmitted rays with consequentimpairment of definition in the image produced by them.

If the rear emulsion is sensitive to rays which should affect only thefront emulsion, such rays should be prevented from reaching the rearemulsion, at least in any material amount. For this purpose the frontcoating may be stained a suitable color, to screen out the undesiredrays, yellow being suitable if the green-sensitive emulsion is in front.Or the support 1 may be stained, or the film may have, as in Fig. 2 atrans parent colored coating or layer between the support 1 and thefront emulsion.

If it is desired to print with the redsensitive emulsion in front thisemulsion must not, of course, be materially affected by the rays whichshould affect the rear coating. This, however, presents no greatdifficulty, as it is well known that with certain derivatives of cyaninean emulsion can be made very sensitive to red and yet be practicallyblind to certain rays in the By using a printing light which has rays ofonly two colors, for example red and green, it is thus possible tosecure satisfactory color renderings with a redsensitive emulsion infront. Of course if such a red-sensitive GIITlllSlOII is used on theback and the printing light has only two colors (say red and green) thegreen rays need not be screened out.

Although, for the best results, the emulsions on the negative stock or.raw film should be, when considered together, sensitive tosubstantially all the colors of the object to be photographed in orderto produce the best condition of orthochromatism in the combinednegative images before staining or coloring the same, the emulsions onthe positive stock need not be; particularly if printed from a two-colornegative of the kind described by means of light of only two colors,corresponding tothe two colors of the negative. Thus the positive can besensitized primarily for the two colors, say red or orange or orange-redon one side and green on the other, or any other two colors that maIy besuitable for the purpose.

n printing positives I prefer, in any case, to use rays of only twocolors, usually red and green. This may be done in various ways, as forexample by employing a light which emits rays of all colors and thenscreening out all but those desired. Thus in Fig. 5 it may be assumedthat rays of all colors are emitted by the source at 17; then to printon the red-sensitive emulsion (3, for instance) a red filter is placedsomewhere between the source and the film A, say at f, and the exposuremade, thereby producing a latent image on the red sensitive emulsion.The red filter is then replaced by one of a suitable green color, topermit green but no red rays to pass, thus producing alatent image onthe green sensitive emulsion. If the two emulsions are of unequal speedthe difference can be easily compensated for by suitable variation inthe intensity of the light. or the duration of the exposure, or both.For example. suppose thatthe red-sensitive emulsion is markedly slowerthan the other. Then in following the procedure described in thepreceding paragraph, the exposure through the red filter can belengthened, or the intensity of the light increased, while the filter isin use, or both the intensity and the time may be increased. Similarcompensatory methods can be used if one or the other of the negativeimages is too weak or too strong, as by reason of under or overexposure, .or under or over development, or is too deeply colored.

- A camera of the type described in my Patent No. 1,208,739, abovereferred to, can be advantageously used for printing positives as wellas for making either type negatives. Such a camera is illustrated inFig. 7, which shows a lens 40 receiving rays 41, 42, 43, transmittedthrough a negative B' hav ing images of the non-congruent type. Afterpassing through the lens the rays impinge upon a transparent reflector44, which reflects part of the rays and transmits part. The reflectedrays proceed to the reflector 45 and finally reach the raw positive filmA while the transmitted portion of the rays are reflected to the otherside of the double coated film by the reflectors 47, 48. In this methodit is not necessary, or even desirable, to have either emulsiontransparent; and in fact, if either issensitive to the rays which shouldafi'ect only the other, the latter should preferably be opaque, at leastto the rays referred to, or positive film stock of the type illustratedin Fig. 2 can be used. In the method illustrated in Fig. 7 the printingcan easily be effected by two-color 'rays.

Filter filter f can be used somewhere between thelight-splittingreflector 44 and the emulsion 2 and a red filter betweenthe reflector 44 and the emulsion 3. A convenient position for thelatter filter is at f, onthe back of the reflector. If necessary ordesirable, particularly when the light projected through the negatiVeB"'is white, a filter f may be used to cut off the violet and ultravioletrays and possibly some of the blue; A similar (not shown) may be usedfor the same purpose in any of the other printing methods.

Another form of camera of the general type described in my prior PatentNo. 1,208,- 739 is illustrated in Fig. 7 In this form, a reflectingprism P is arranged behind the lens 49 and covers about half of thelatter. Half of the rays from the negative B through the lens 49 arereflected by the surface p to a reflector 50 and by the latter arereflected to the positive film A, which is arranged at an angle to theaxis of the lens for the purpose of economizing space so that a lens ofshorter equivalent focal length can be use The other half of the raysare reflected by a reflector 51 to the other side of the positive film AThe prism P has preferably such angles, and is so positioned, that therays which pass through it will enter and emerge at substantially rightangles to the front and rear surfaces respectively,

and if the reflection at the surface 2 is not total the said surface maybe silvered in the usual way. Though differing in specific structurefrom that shown in Fig. 7, the camera shown in Fig. 7 can be used inexactly the same way as the former. The mirrors 50 and 51 can beadjusted by any convenient means. For example the mirror 51 can beturned on the pivot 51* by a tangent screw such as shown at 52. Themirror 50 is shown as provided with a boss 53 pivoted between two lugs54 so as to be pivotally adjustable by means of a tangent-screw shown inplan at 55. The lugs 54 are mounted on a member 56 (shown in dottedlines) which is slidable in guides 57. (also shown in dotted lines),toward and from the film A, by means of a screw 58. y

If the film or support for the two images is not transparent the imagescan be projected by reflection, as for example by means of apparatussuch as the camera shown in ig. 7 or Fig. 7 In such method of projectionthe two images are illuminated in any convenient manner, not shown, andthe rays reflected by the images are projected by the lens upon thescreen. I prefer, however, the method in which the projecting rays passthrough the images and the support thereof.

In printin cinemato raphic positives the negatives an posltlve lms arein the form the printing light.

When the exposed positive stock is developed (in any convenient way!)the positive images are produced, one on each side of the film, thenature of which images can best be explained by reverting to the colornegative described above and noting what it does to This negative, itwill be remembered, shows by transmitted light a red circle on abackground of which the upper half is green and the lower half issubstantially opaque, or black; because on one side the lower half isred and on the other side is green. Now, when the printin light strikesthe negative, red rays (and red rays only) will pass being stoppedelsewhere Which is green on one side, at the bottom and at the top.Hence when the positive is developed, the red-sensitive emulsion willhave a deposit in circular form, but the background will be transparent.On the other hand, the green printing-rays are stopped by the red circleand by the lower half of the background on the red side of the negativefilm; but they pass through the upper half of the background, which isgreen on one side and colorless on the other. Hence on thegreen-sensitive side the positive will have an image of the upper halfof the background while the lower half, and the circle, will betransparent. Viewed by transparent light, or projected upon a screen,the two images combine to form a single or unitary image, which imagemay or may not be a strictly correct rendering, in monochrome, of thecolors of the object according to their visual luminosities.

From the foregoing it will be seen that the two images arecomplementary, in the sense that neither correctly represents the entireobject and that each completes the other, so to speak.

The positive having been produced in monochrome, the deposits formingthe two images are colored in substantial correspondence with the colorsor groups of colors which they are to transmit. For example, -thedeposit on the green side is changed from black to blue-green and thaton the red side to red. Then upon viewing the film by transmitted whitelight or by the background,

by projection with white light, the circle through the circle,

used, depending upon the effects desired, but in general I prefer greenor blue-green, and red or orange-red.

If the positive film just described is of the type having non-congruentimages, that is, on larger than the other so that when projected byconverging rays the two images will combine on the screen to produce asingle or unitary image, the film will appear as in Fig. 7". It will beobserved inFig. 7 that the red circle 7" (on the upper side) is largerthan the corresponding image 1" on the other side of the film. It willof course be understood that the difference in size of the images ismuch exaggerated. In motion picture film for use.

with a projection lens having a focal length of a few inches thedifference in size of the two images can hardly be detected with thenaked eye, even at the extreme corners of the film.

If the two pictures or images are taken through the same lens, they aretaken from the same point of view and hence are devoid of the parallaxeffects which are produced when two lenses are employed; and if they aretaken simultaneously, a moving object appears in exactly the sameposition in both pictures or images. It will, moreover, be observed thatthe pictures are in successive pairs, so to speak, each picture of oneseries being paired with one of the other series,

and it will also be seen that throughout the series of pairs, there isthe same degree of accuracy of registration. In other words, thepictures forming one pair are registered to the same degree of accuracyas are the pictures of the preceding or the succeeding pair. Thiscondition follows both from the nature of the negative film from whichthe positive was printed and from the fact that the two series ofpictures on the positive are in fixed relation, each to each, and hencecannot shift relatively to each other in the pro ector.

The coloring of the positive film may be efiected in any suitable way.The method which I prefer at the present time is to treat both sideswith an aqueous solution of iodin and potassium iodid to convert thedeposited silver into silver iodid, then treat the two sides with basicdyes of the desired colors. The silver iodid is then dissolved out withpotassium cyanid or. with an alum bath containing tannin or tartaremetic, the action of these substances preventing the dye washing out.The film is then washed, leaving the images colored but transparent.

The exposed gelatin on one or both sides of the film can be stained alight yellow. This would tend to improve the color rendermg,particularly in respect to green, for if the yellow staining is resortedto the image on the green side can be colored a lighter blue-green or amore blueishbluegreen and still give good greens when the other side iscolored orange-red. The highlights would then have a yellowish tinge,but scarcely to a noticeable extent especially when th film is projectedin a darkened room. 7

Other methods may be used to produce the positive, as for example themethod described in my Patent N 0. 1,228,877 issued June 5, 1917. Inthis method two films are placed face to face or back to back (and, ifdesired, fastened together along one edge) and are perforatedsimultaneously. They are then exposed in a camera of the type describedin my Patent No. 1,208,739, hereinbefore mentioned, the films beingpassed in unison through the same film gate, to produce on one film aseries of negatlve images by light of one color or group of colors andin the other a complementary series by light of another color or groupof colors. After exposure the two films are developed and fixed in theordinary way, and the positive film, coated on both sides withlight-sensitive emulsions, is placed between the two and printed bylight passing through the negatives from both sides. If the negativefilms were back to back in the camera they are preferably turned overfor printing, so that the images will be in.

contact with the emulsions on the positive film. Registry in printing issecured by means of pins fitting in the perforations which weresimultaneously made in the negative films. Consequently the images onthe opposite sides of the positive film are registered with accuracy.

A type of negative film is illustrated in Figs. 10 and 11 comprisingfour separable parts, the negative films 118 and 120 with the sensitizedsurfaces 119 and 121 on the inside, a spacer 128 and separator 122. Thefilm is perforated for the standard holes 130, 130 on both sides, but iscut with an additional margin in which the holes 131, 131 are. punched,preferably simultaneously, through both films and the spacer 129. Afterexposure the films are separated, developed and fixed and stained (ifdesired) and are then reassembled with the spacer between them exactlyas they were before exposure with the. pins in place and the positivefilm placed between and printed by light from both sides.

What I claim is 1. A cinematographic positive for the projection ofunitary images in substantially the natural colors of the object orobjects represented, comprising a strip of film bearing twocomplementary series of differently colored monochrome images, oneseries on each side, the images on one side being paired with thecorresponding images on the other, the images of each pair beingcongruent at one point but progressively different in size from suchpoint to the margins.

2. A cinematographic positive for the projection of picturesrepresenting successive phases of an object in motion, consisting of atransparent film bearing on its opposite sides two series of coloredpositive images, one series on each side; the images of one series beingcomplementary to those of the other, and difi'erently colored; and.

the images of the two series being centrally congruent with each otherbut progressively difl erent in size from the center to the margins.

In testimony whereof I aflix my signa- 15 ture in the presence of twosubscribing Witnesses.

PERCY D. BREWSTER.

Witnesses:

M. LAWSON DYAR, S. S. DUNHAM.

